Mysticete Species Research Articles

Examination of Isotopic Signals to Determine Trophic Dynamics and Diet of Gulf of Maine Mysticetes Prior to an Oceanographic Regime Shift

Stable isotope analysis (SIA) is a useful tool to assess the health and foraging habits of large marine predators, metabolic stress, pregnancy, and migration patterns. This study provides baseline SIA data for four Gulf of Maine mysticete species and serves as a benchmark for future assessments. SIA was conducted on skin biopsies collected in two time periods: 1988 to 1992 (n = 15) and 1999 to 2005 (n = 187). Samples were collected from humpback whales (Megaptera novaeangliae; n = 116), fin whales (Balaenoptera physalus; n = 74), minke whales (Balaenoptera acutorostrata; n = 6), and North Atlantic right whales (Eubalaena glacialis; n = 6). There were statistically significant differences in isotopic value among species, years, and regions sampled. By species, North Atlantic right whale δ13C and δ15N levels were significantly different than the other species analyzed. Additionally, humpback whales had a δ15N value that was significantly higher than the value found in fin whales. By date, humpback whales showed significant difference in δ13C in 2002 from the two previous years. For fin whales, 2002 showed significant difference in δ13C for all other years’ samples (2000 to 2003). By region, two regions that were the greatest distance apart (Bay of Fundy and Great South Channel) showed significant differences in δ13C for humpback whales. Demographic analyses for humpback and fin whales found a significant difference between calves versus other age classes, presumably due to nursing. A decadal comparison of humpback whales at one site (Stellwagen Bank) found no significant difference between decades. This dataset provides a benchmark for stable isotope measurements in large baleen whales for this regional ecosystem.

Evolutionary novelties underlie sound production in baleen whales.

Baleen whales (mysticetes) use vocalizations to mediate their complex social and reproductive behaviours in vast, opaque marine environments1. Adapting to an obligate aquatic lifestyle demanded fundamental physiological changes to efficiently produce sound, including laryngeal specializations2-4. Whereas toothed whales (odontocetes) evolved a nasal vocal organ5, mysticetes have been thought to use the larynx for sound production1,6-8. However, there has been no direct demonstration that the mysticete larynx can phonate, or if it does, how it produces the great diversity of mysticete sounds9. Here we combine experiments on the excised larynx of three mysticete species with detailed anatomy and computational models to show that mysticetes evolved unique laryngeal structures for sound production. These structures allow some of the largest animals that ever lived to efficiently produce frequency-modulated, low-frequency calls. Furthermore, we show that this phonation mechanism is likely to be ancestral to all mysticetes and shares its fundamental physical basis with most terrestrial mammals, including humans10, birds11, and their closest relatives, odontocetes5. However, these laryngeal structures set insurmountable physiological limits to the frequency range and depth of their vocalizations, preventing them from escaping anthropogenic vessel noise12,13 and communicating at great depths14, thereby greatly reducing their active communication range.

Cetacean strandings in San Diego County, California, USA: 1851–2008

There were 717 cetacean strandings recorded in San Diego County, California, USA between 1851 and 2008. These strandings comprised 18 odontocete and 6 mysticete species. Common dolphins (both the short-beaked (Delphinus delphis) and long-beaked common dolphin (D. capensis)) were the most commonly stranded cetacean species (43.2%), followed by bottlenose dolphins (Tursiops truncatus) (16.5%), gray whales (Eschrictius robustus) (11.0%), and Pacific white-sided dolphins (Lagenorhyncus obliquidens) (7.0%). A higher number of strandings was observed in the La Jolla and Coronado/Imperial Beach areas, which likely reflects the influence of coastal protrusions in those regions. Strandings of bottlenose dolphin neonates suggests their calving season extends from May to September. Strandings of common dolphin species peaked in the early- to mid-1970s and in the late-1990s to 2008, coincident with cool oceanographic regimes. In addition, extralimital strandings of harbour porpoises and temporal changes in stranding rates of Dall’s porpoises (Phocoenoides dalli) and short-finned pilot whales (Globicephala macrorhynchus) may have been associated with changes in oceanographic conditions. Evidence of human interaction in strandings included entanglements, boat strikes, shootings and harpooning. Overall, the stranding record largely reflected the species composition of the Southern California Bight and provided confirmation for presence of cryptic species not previously recorded by aerial and ship surveys.

Biologically Important Areas II for cetaceans within U.S. and adjacent waters – Hawaiʻi Region

In this assessment we incorporated published and unpublished information to delineate and score Biologically Important Areas (BIAs) for cetaceans in the Hawaiʻi region following standardized criteria. Twenty-six cetacean species have been documented in Hawaiʻi. Eleven odontocete species have distinct small populations resident to one or more island areas: rough-toothed dolphins, pantropical spotted dolphins, common bottlenose dolphins, spinner dolphins, short-finned pilot whales, false killer whales, pygmy killer whales, melon-headed whales, Blainville’s beaked whales, Cuvier’s beaked whales, and dwarf sperm whales. Eight species of mysticetes have been documented, although their occurrence and behavior are poorly understood, with the exception of breeding humpback whales and, more recently, common minke whales. Thirty-five BIAs were delineated or revised from the initial 2015 effort: 33 for small and resident odontocete populations and two for humpback whale reproductive areas. Hierarchical BIAs reflecting core areas of use or population-specific ranges were delineated for nine species. Reproductive watch list areas were designated for common minke whales in the main Hawaiian Islands (MHI) and humpback whales in the Northwestern Hawaiian Islands (NWHI); these areas did not meet the criteria for a BIA due to limited supporting information. All but three BIAs were in the MHI, reflecting the disparities in research effort between this region and the NWHI. Spatial extents of BIA boundaries ranged from 457 km2to 138,001 km2(median = 8,299 km2). Scores (range: 1-3) for Data Support and Boundary Certainty were moderate to high (mean = 2.40 and 2.43, respectively), while Intensity and Importance scores were slightly lower (mean = 1.94 and 1.89, respectively). Many of the Hawaiʻi species have been extensively studied over several decades; accordingly, this region ranks among the highest in terms of Data Support relative to other regions. BIAs presented here describe known ranges of small resident populations, intensities of use, and uncertainties in important areas for cetaceans in Hawaiʻi based on the best available data, and have also revealed knowledge gaps to guide future research efforts.

Influence of anthropogenic activities on marine mammal strandings in the estuary and northwestern Gulf of St. Lawrence, Quebec, Canada, 1994–2008

Stranding records have long been used to monitor marine mammal mortalities and to help identify threats to populations. In coastal areas, marinemammals face numerous anthropogenic threats such as marine traffic and commercial fishing. The objective of this study was to investigate marinemammal stranding records from the St. Lawrence Estuary (SLE) and the northwestern Gulf of St. Lawrence (NWGSL), Quebec, Canada from 1994to 2008 for evidence of anthropogenic trauma caused by entanglement in fishing gear, ship collisions and gunshots. Of 1,590 marine mammalstranding records, 12% (n = 192) had evidence of anthropogenic trauma, most incidents being reported during summer when activities such asmarine traffic, most commercial fishing and recreational boating, occurred and a greater number of species were present in the area. These incidentswere classified into five categories (Incidental catch, Ship collision, Severe injury, Gunshot, Other). There were 1,245 mortalities and observationson carcasses suggested that anthropogenic trauma led to the death of 11% (141/1,245) of marine mammals: 14% (87/627) of cetaceans and 9%(54/618) of seals. Mortality of seals due to anthropogenic trauma was low, involving mainly Gunshot for grey (26% or 8/31) and harbour seals(26% or 8/31). Over the study period, marine mammal incidents with evidence of anthropogenic trauma increased significantly, driven by an increasein Incidental catch for two mysticete species, the common minke whale, 42% (39/92) and humpback whale, 13% (12/92) and Other for harbourporpoise 67% (16/24). Ship collision was the most common anthropogenic trauma for fin whales (22% or 8/36) and SLE beluga5 (22% or 8/36).Severe injury was reported for 22% (2/9) of small cetaceans and 78% (7/9) of seals. Evidence from some harbour porpoise stranding records(categorised as Other) suggests illegal hunting, incidental catch, predation or scavenging by grey seals in a marine protected area. The observedincrease in Incidental catch of common minke and humpback whales may be due to: (1) a shift in distribution of these two species into the SLE andNWGSL, possibly related to changes in the ecosystem; (2) changes in fishery practices; and (3) an increase in detection of marine mammal strandings.Anthropogenic trauma affecting marine mammals was documented including some species at risk, such as the harbour porpoise, the St. LawrenceEstuary beluga population, blue and North Atlantic right whales, in the St. Lawrence ecosystem including in a marine protected area. This studydemonstrates the usefulness of stranding records in helping to monitor human-caused mortality in marine mammal populations.

On the rise: Climate change in New Zealand will cause sperm and blue whales to seek higher latitudes

Climate impacts affect marine ecosystems worldwide with island nations such as New Zealand being extremely vulnerable because of their socio-economic and cultural dependence on the marine and costal environment. Cetaceans are ideal indicator species of ecosystem change and ocean health given their extended life span and cosmopolitan distribution, but limited data availability prevents anticipating change in distribution under future climate changes. We projected the range shifts of a key odontocete and mysticete species (Physeter macrocephalus and Balaenoptera musculus) in 2100 relative to present day in New Zealand waters, using an ensemble modelling approach, under three climate change scenarios of different severity.The results show a latitudinal shift in suitable habitat for both whale species, increasing in magnitude with severity of sea surface temperature warming. The most severe climate change scenario tested generated 61% and 42% loss and decrease of currently suitable habitat for sperm and blue whales, respectively, mostly in New Zealand’s northern waters. These predicted changes will have a strong impact on the ecosystem functioning and services in New Zealand’s northern waters but also in coastal areas (critical for the species’ foraging and survival). Not only do these simulated range shifts help to identify future potential climate refugia to mitigate a global warming, they also generate a range of socioeconomic consequences for island nations relying on wildlife tourism, industry, and environmental protection.

Forty-year historical analysis of marine mammal strandings in Texas, from 1980 – 2019

Long-term trends in marine mammal stranding patterns can provide useful information on basic life history parameters, spatiotemporal distribution, natural and human-related mortality events, and potentially vulnerable populations. Between 1980 and 2019, a total of 5,301 marine mammal strandings were recorded in Texas, USA. In total, 23 species were identified, including 19 odontocete species (toothed whales and dolphins), 3 mysticete species (baleen whales), and 1 sirenian species (manatee). Common bottlenose dolphins (Tursiops truncatus) stranded most frequently (94%). Six unusual mortality events occurred with causes attributed to disease, harmful algal blooms, or unknown etiologies. Common bottlenose dolphin stranding events increased significantly in late winter/early spring, with an early onset in southern Texas, and had a consistent peak in March involving primarily calves and adults. Spatial analyses using kernel density estimation within seven coastal Texas stock management areas, delineated by the National Marine Fisheries Service, identified potential hotspots for common bottlenose dolphin strandings near higher human population density and deep water channels. Peak stranding density estimates in each stock area ranged from 0.32 – 4.6km-2 for presumed bay, sound and estuarine (BSE) stocks and 0.82km-2 for the presumed Western Gulf of Mexico Coastal Stock. Common bottlenose dolphin stranding events were positively male-biased, including a significantly higher number of stranded male fetuses and neonates, and sexual dimorphism was observed in total body length of adults, with significantly greater length in males. For all records where human interaction (HI) could be determined as ‘yes’ or ‘no’, 30% were positive for HI, with the highest proportion of HI events occurring in the central and southern-most BSE stock areas; however, it is unknown how many HI cases contributed to mortality. This longitudinal study provides a comprehensive overview of marine mammal stranding patterns in Texas and serves as a useful resource for stranding investigators and Gulf-wide natural resource managers.

Anatomical Mechanism for Protecting the Airway in Whales Involves Interlocking the Larynx

The mammalian respiratory and digestive tracts are configured to enable simultaneous function of both systems, while preventing accidental choking on food. This protection is critical in mysticetes (baleen whales), especially as feeding involves large pressures and potential inundation of water.Dissections were performed on 43 specimens representing 8 mysticete species: fin, blue, sei, minke, humpback, gray, right, and pygmy right whales. 36 specimens were necropsied as whole carcasses, 5 were obtained as whole heads, 2 were whole fetuses. All were recovered post mortem from US beach strandings. Dissections focused on hyolaryngeal anatomy, soft palate, and nasopharynx.Results indicate that the mysticete larynx retains an intranarial position during feeding, swallowing, breathing, and sound production. The soft palate forms a muscular ring that keeps the larynx interlocked into the nasopharynx. The epiglottis overlaps the soft palate extensively, nesting rostrally over a shelf that forms a pocket lined by nasopharyngeal pits. The soft palate articulates tightly with the epiglottic base, and lateral portions arc around larynx to meet in the caudal midline. Posteriorly, the soft palate forms another smaller shelf that interlocks with the caudally curling paired corniculate cartilages. These two points of interlocking keep the larynx intranarially positioned during deglutition. The paired lateral food channels (piriform sinuses) pass on either side of the epiglottis and corniculate cartilages and unite caudally to form the esophagus. Food can easily pass around the interlocked larynx using these lateral food channels.Suprahyoid muscles elevate the oral floor, squeezing out water and pushing the tongue towards the oral roof to compress the food bolus and force it through the oropharyngeal inlet. The oropharyngeal inlet appears regulated by muscles that likely relax to allow dilation. Suprahyoid muscles also ensure the larynx‐soft palate interlock, as the epiglottis is pushed rostrally to maximally overlap the soft palate. Food encountering the interlocked soft palate‐epiglottis is diverted laterally into paired lateral food channels. Infrahyoid muscles retract the larynx caudally, returning it to its rest position with moderate soft palate overlap. Continued contraction would allow the long epiglottis to slide along its overlap with the soft palate, giving mobility to enlarge the depth of the lateral food channels if necessary, without unlocking the larynx. This interlock preserves the protection of the airway.Unlocking the epiglottis necessitates elevating the soft palate while withdrawing the epiglottis. This may occur to channel air into the oral cavity for bubble cloud production. However, the larynx is at risk of inundation from water in this position, as it forms a very poor seal with the corniculate cartilages and their flexible flaps. The rigid epiglottis could not be folded caudally manually to meet the corniculates. No muscles were noted that could retract the epiglottis towards the corniculates. Similarly, no muscles were found that could rigidify the corniculate flaps or cause them to seal in opposition. Therefore, the sealing mechanism of the larynx is limited to opposition of the arytenoid cartilages supporting the U‐shaped vocal fold.

Feeling for food: Can rostro-mental hair arrays sense hydrodynamic cues for foraging North Atlantic right whales?

North Atlantic right whales (NARWs; Eubalaena glacialis) possess an arrangement of fine hairs on the rostrum and chin that may be used for hydrodynamic sensing during feeding. These hairs occur across mysticete species and are known to possess adequate innervation in the subdermal follicle to support their consideration as sensory hairs (vibrissae). However, the small size of the hair structure with respect to the enormous scale of the animal's body has caused doubts regarding their utility and prompted speculation that the hairs may be vestigial or minimally functional. Here we show that NARW hairs occur in abundance on the leading surface of the head in a unique and characteristic arrangement. We consider the sensory hairs in context of the fluid environment in which this species forages and argue that the size of the hair is scaled to the size of the animal's small planktonic prey, thus suggesting that the hairs play an important role in the sensory ecology of these animals.

The unique rectus extraocular muscles of cetaceans: Homologies and possible functions.

Each rectus extraocular muscle in cetaceans divides into two portions: a massive palpebral belly that inserts into the deep surface of the eyelids and a smaller scleral belly that inserts onto the eyeball. While the cetacean palpebral insertions have long been recognized, their homologies and functions remain unclear. To compare cetacean rectus EOM insertions with the global and orbital rectus EOM insertions of other mammals we dissected orbital contents of 20 odontocete species, 2 mysticete species and 18 non-cetacean species, both aquatic and terrestrial. Four cetacean species were also examined with magnetic resonance imaging (MRI). All four rectus muscles in cetaceans had well-developed palpebral bellies and insertions. Adjacent palpebral bellies showed varying degrees of fusion, from near independence to near complete fusion. Fusion was most complete towards palpebral insertions and less towards origins. A medial moiety of the superior rectus palpebral belly is likely the levator palpebrae superioris. Smaller but still robust scleral insertions were present on all recti, with the medial rectus (MR) being significantly more muscular than the others. All non-cetacean species examined had recti with distinct global and orbital insertions, the latter generally onto Tenon's capsule. Orbital insertions in pygmy hippopotamus and Florida manatee extended into the deep surfaces of the eyelids, hence qualifying as palpebral insertions. Our results suggest that rectus EOMs of mammals generally have both global and orbital insertions, and that palpebral bellies of cetaceans and other species are modified homologs of the orbital insertions. The presence of palpebral insertions in pygmy hippopotamus and absence in other cetartiodactyls suggests an intermediate condition between terrestrial cetartiodactyls and cetaceans. Palpebral insertions in Florida manatee and reports of their presence in some pinnipeds suggest parallel evolution in multiple aquatic lineages. Various functions of cetacean palpebral recti have been proposed, including eyelid dilators, protection during diving and thermogenesis for warming eye and brain. For further insight into their possible functions, we observed eye movements of captive bottlenose dolphins (Tursiops truncatus) at the U.S. National Aquarium. Our observations showed that in addition to rotation of the eyeball the entire surrounding palpebral region also moves during gaze changes. For example during upward gaze the globe not only rotates in supraduction but translates dorsally as well. It appears the rectus palpebral bellies are responsible for flexing the palpebral structures and thus also translating the globe, while the scleral insertions act directly for ocular rotation. Along with frequent non-conjugate eye movements, the oculomotor mechanics and repertoire of cetaceans are thus quite distinctive. Summarily, axial displacement within the orbit is a major 'eye movement' in cetaceans, with protrusion and retraction mediated by well-developed circular muscles and retractor bulbi respectively. Torsional eye movements driven by elaborate oblique EOMs are likewise significant. The roles of rectus EOMs for ocular rotation via their scleral insertions, especially the highly muscular MR, are for typical supra/infraductions and nasal/temporal ductions. The palpebral bellies accentuate these ductions by translating the globe and surrounding structures in the same direction.

Killer whale predatory scarring on mysticetes: A comparison of rake marks among blue, humpback, and gray whales in the eastern North Pacific

AbstractWe investigated the predator–prey relationship between baleen whales and killer whales by observing predatory scarring (rake marks) on the tail flukes of three mysticete species from the eastern North Pacific Ocean: humpback, blue, and gray whales. We integrated both qualitative scores and new quantitative measures to compare predatory scarring left by killer whales on the three species. We found statistically significant interspecies differences in incidence, location, and accumulation rates of scarring. Gray whales showed a higher incidence of predatory scarring compared to the other two species. Humpback and gray whales bore most of their rake marks on the trailing edge of the tail fluke, while blue whales showed more evidence of predatory scarring on the leading edge of the fluke, potentially consistent with previously hypothesized theories of flee versus fight responses to killer whales for different mysticete species. Of whales with scarring, blue whales were twice as likely to suffer from fluke mutilation compared to humpback and gray whales. Humpback and gray whales were also significantly more likely to accumulate new rake marks over the years compared to blue whales. We examine how these differences provide insight into the prey‐specific hunting behavior of killer whales.

Cetacean occurrence offshore of Washington from long-term passive acoustic monitoring

A variety of cetacean species inhabit the productive waters offshore of Washington State, USA. Although the general presence of many of these species has been documented in this region, our understanding of fine-scale habitat use is limited. Here, passive acoustic monitoring was used to investigate the spatial and temporal distributions of ten cetacean species at three locations offshore of Washington. Between 2004 and 2013, a total of 2845 days of recordings were collected from sites on the continental shelf and slope, and in a submarine canyon. Acoustic presence was higher for all species at sites farther offshore. Detections were highest during the fall and winter for blue (Balaenoptera musculus), fin (B. physalus), and humpback whales (Megaptera novaeangliae), likely related to reproductive behavior, while minke whales (B. acutorostrata) were only detected on two days. Odontocetes showed temporal separation, with sperm whale (Physeter macrocephalus) detections highest in spring, Risso’s (Grampus griseus) and Pacific white-sided dolphins (Lagenorhynchus obliquidens) highest in summer, and Stejneger’s beaked whales (Mesoplodon stejnegeri), Cuvier’s beaked whales (Ziphius cavirostris), and the BW37V signal type highest in winter or spring. There was interannual variation in detections for most mysticete species, which may be linked to oceanographic conditions: blue and fin whale detections increased during 2007 and 2008, and fin and humpback whale detections increased in 2011. These results inform our understanding of cetacean behavior and habitat use in this region and may aid in the development of conservation strategies suited to the dynamic conditions that drive cetacean distribution.

In-situ observations of the sensory hairs of Antarctic minke whales (Balaenoptera bonaerensis).

The sense of touch in the largest marine mammals is poorly understood. While mysticetes possess specialized sensory hairs that are present through adulthood, descriptions of these structures are based almost entirely on examination of tissues in post-mortem individuals. Sensory hairs have rarely been observed and described in living whales. We photographed Antarctic minke whales Balaenoptera bonaerensis in the Western Antarctic Peninsula and used high-resolution images to describe the number, distribution, orientation, and relative size of sensory hairs in freely swimming individuals. Sensory hairs were well developed. They were distributed on the tip of the lower jaw, the margins of the upper and lower jaw, and near the blowhole. Far fewer hairs were observed than reported for other mysticete species, including the related species Balaenoptera acutorostrata. Placement and apparent stiffness of sensory hairs within living tissue combined with observations and images of moving whales suggest these structures aid in detecting air and ice interfaces, and possibly, the boundaries of submerged prey fields.

Monitoring the acoustic ecology of the shelf break of Georges Bank, Northwestern Atlantic Ocean: New approaches to visualizing complex acoustic data

Within a soundscape, anthropogenic sound often dominates frequency ranges used by various species, leading to signal overlap and potential communication masking. The acoustic niche hypothesis predicts species will avoid competition by vocalizing at unique bandwidths. To evaluate the extent of anthropogenic overlap, it’s helpful to understand acoustic niches across time. This study aims to assess the co-occurrence of cetaceans and anthropogenic activities, presenting simple and accessible visualizations of the temporal and spectral overlap. Continuous passive acoustic recordings from 10 Hz to 100 kHz were collected near three deep-water canyons (Heezen, Oceanographer, and Nantucket) along the continental shelf break of Georges Bank between April 2015 and March 2016. Daily presence was documented for five mysticete species (North Atlantic right, fin, blue, sei, humpback), five odontocete species and/or groups combined according to primary frequency ranges (delphinids, sperm whales, Kogia spp, Sowerby’s, and Cuviers’/True’s/Gervais’ beaked whales), and four anthropogenic activities (airgun noise, broadband ship noise, echosounders, and explosions). At each site, cetacean and anthropogenic sources were found to be significant contributors. Individual cetacean species/groups were present from 2% to 100% of days across sites, with delphinids, sperm whales, and fin whales detected most consistently. Airgun noise, the most frequently detected anthropogenic signal, ranged from 50% to 91% of days across all sites, followed by broadband ship noise (15–65% of days), echosounders (1–14% of days), and one explosion detected at Oceanographer Canyon. This approach allows for broad comparison of species and anthropogenic activity, providing understanding of variability in acoustic overlap and potential masking between sites.

Cetacean occurrence and diversity in whale-watching waters off Mirissa, Southern Sri Lanka.

Scientific information is vital to the conservation of cetaceans and the management of whale-watching activities. The southern coastal waters of Sri Lanka are near a narrow continental shelf and biologically abundant in cetacean species. Although the occurrence of cetaceans has been investigated in certain waters of Sri Lanka, few surveys have been conducted along the southern coast. To fill this gap, we conducted boat-based surveys from January to May 2017 to investigate the occurrence, diversity, and behavior of cetaceans in the waters off Mirissa, covering a survey area of 788.9 km2 . During 55 survey days, we recorded a total of 242 cetacean sightings and identified at least 9 species (3 mysticetes and 6 odontocetes). The blue whale was the most common mysticete species (167 of 174 mysticete encounters), followed by the Omura's whale (4 of 174) and Bryde's whale (3 of 174). The spinner dolphin was the most common odontocete species (28 of 68 odontocete encounters), followed by the sperm whale (18 of 68), common bottlenose dolphin (13 of 68), short-finned pilot whale (5 of 68), melon-headed whale (2 of 68), and killer whale. Blue whales and sperm whales exhibited a clear preference for outer shelf and high slope areas, and blue whales were observed feeding along these waters. The present study provides near-baseline information on cetacean occurrence and diversity in whale-watching waters off southern Sri Lanka, and highlights the urgent need for proper management strategies for whale-watching activities.

A new balaenopterid species from the Southern North Sea Basin informs about phylogeny and taxonomy of Burtinopsis and Protororqualus (Cetacea, Mysticeti, Balaenopteridae)

Background An extensive radiation can be inferred among balaenopterid mysticetes in the last 10 million years based on a rich fossil record. Many extinct genera and species have been established in the past by the study of fossil rorquals from northern and southern hemispheres. In many cases, the new fossils are used to create new genera. However, in very recent times, new species of known genera have been described that help our understanding of the speciation processes and the biogeography of these whales. Here, a new species of balaenopterid whales is described in order to better understand the past diversity of Balaenopteridae and to analyze its paleobiogeographical implications. As the new species closely resembles a taxon established in the 19th century (i.e., Burtinopsis), a detailed analysis of this taxon was necessary to support the new taxonomic statements of this article. Methods A new partial skeleton including skull and earbones is described and compared to an extended sample of living and fossil mysticete species. A phylogenetic analysis including 355 character states scored in 88 taxa was performed to understand its relationships within the genus Protororqualus, to allow paleobiogeographic inferences and to better understand the relationships of Protororqualus within Balaenopteridae. Maximum parsimony analyses of character evolution were performed to understand morphological transformations within Balaenopteridae. The revision of Burtinopsis was carried out based on detailed descriptions and comparisons of the type materials that were figured and measured. Results Protororqualus wilfriedneesi sp. nov. was established based on a comparative analysis of the skull and earbone morphology. The specimen is dated back to the Zanclean (Lower Pliocene, between c. 5.3 and 3.6 Ma). A taphonomical study of the holotype skeleton revealed evidence of interactions with sharks and fishes before the definitive burial of the carcass. Based on the phylogenetic analysis, the monophyly of the genus Protororqualus was confirmed. Protororqualus wilfriedneesi sp. nov. was more derived than Protororqualus cuvieri suggesting that it resulted from an invasion of the North Sea Basin (and the North Atlantic ocean) from the Mediterranean basin. Several specimens from western and eastern sides of the Atlantic Ocean are described that suggest that Protororqualus wilfriedneesi had a trans-Atlantic distribution in the Pliocene.

Baleen turnover and gut transit in mysticete whales and its environmental implications

Baleen, a unique oral α-keratin, has flat cortical layers enclosing hollow horn tubules. Baleen grows continuously to replace erosive loss from feeding-related wear. This is essential for maintaining efficient filtration over a whale’s long life history. Baleen fragments are seen in stomach contents and feces. We focused on fin (Balaenoptera physalus) and bowhead whales (Balaena mysticetus), but examined eleven mysticete species. Histological features including variably sized tubules plus differential growth along plate axes (growing faster along the medial fringed edge) and between plates of a rack (central plates growing faster than others) relate to baleen strength and flexibility. Sheet-like cortical layers provide strength and probably hinder erosive shedding, whereas medullary (tubular/intertubular) keratin provides flexibility and likely promotes shedding. To calculate amounts of grown/lost baleen, we considered both erosive wear and basal growth, recognizing that each plate represents several years of growth. We estimate average annual loss of 70–100,000 cm2 (20–40,000 cm3) of baleen in balaenids and 25–50,000 cm2 (7–14,000 cm3) in balaenopterids. Baleen growth rates depend on age, size, and other life history parameters; the most reliable calculations come from morphometric data with plate dimensions measured along full racks. We argue that baleen turnover has been under-rated and baleen growth rates underestimated in the published literature. Baleen turnover maintains filter integrity/porosity, while gut passage possibly clears gastrointestinal tracts of endoparasites. Large volumes of shed keratin hold potential ecological consequences by providing food for microbial decomposers and detritivores throughout ocean ecosystems, especially in polar regions where most mysticete feeding occurs.

Managing the Effects of Noise From Ship Traffic, Seismic Surveying and Construction on Marine Mammals in Antarctica

The Protocol on Environmental Protection of the Antarctic Treaty stipulates that the protection of the Antarctic environment and associated ecosystems be considered in the planning and conducting of all activities in the Antarctic Treaty area. One of the key pollutants created by human activities in the Antarctic is noise, primarily caused by ship traffic (from tourism, fisheries, and research), but also by geophysical research (e.g., seismic surveys) and by research station support activities (including construction). Arguably, amongst the species most vulnerable to noise are marine mammals since they specialise in using sound for communication, navigation and foraging, and therefore have evolved the highest auditory sensitivity among marine organisms. Reported effects of noise on marine mammals in lower-latitude oceans include stress, behavioural changes such as avoidance, auditory masking, hearing threshold shifts, and—in extreme cases—death. Eight mysticete species, 10 odontocete species, and six pinniped species occur south of 60OS (i.e., in the Southern Ocean). For many of these, the Southern Ocean is a key area for foraging and reproduction. Yet, little is known about how these species are affected by noise. We review the current prevalence of anthropogenic noise and the distribution of marine mammals in the Southern Ocean, and the current research gaps that prevent us from accurately assessing noise impacts on Antarctic marine mammals. A questionnaire given to 29 international experts on marine mammals revealed a variety of research needs. Those that received the highest rankings were 1) improved data on abundance and distribution of Antarctic marine mammals, 2) hearing data for Antarctic marine mammals, in particular a mysticete audiogram, and 3) an assessment of the effectiveness of various noise mitigation options. The management need with the highest score was a refinement of noise exposure criteria. Environmental evaluations are a requirement before conducting activities in the Antarctic. Because of a lack of scientific data on impacts, requirements and noise thresholds often vary between countries that conduct these evaluations, leading to different standards across countries. Addressing the identified research needs will help to implement informed and reasonable thresholds for noise production in the Antarctic and help to protect the Antarctic environment.

Prenatal developmental sequence of the skull of minke whales and its implications for the evolution of mysticetes and the teeth‐to‐baleen transition

Baleen whales (Mysticeti) have an extraordinary fossil record documenting the transition from toothed raptorial taxa to modern species that bear baleen plates, keratinous bristles employed in filter-feeding. Remnants of their toothed ancestry can be found in their ontogeny, as they still develop tooth germs in utero. Understanding the developmental transition from teeth to baleen and the associated skull modifications in prenatal specimens of extant species can enhance our understanding of the evolutionary history of this lineage by using ontogeny as a relative proxy of the evolutionary changes observed in the fossil record. Although at present very little information is available on prenatal development of baleen whales, especially regarding tooth resorption and baleen formation, due to a lack of specimens. Here I present the first detailed description of prenatal specimens of minke whales (Balaenoptera acutorostrata and Balaenoptera bonaerensis), focusing on the skull anatomy and tooth germ development, resorption, and baleen growth. The ontogenetic sequence described consists of 10 specimens of both minke whale species, from the earliest fetal stages to full term. The internal skull anatomy of the specimens was visualized using traditional and iodine-enhanced computed tomography scanning. These high-quality data allow detailed description of skull development both qualitatively and quantitatively using three-dimensional landmark analysis. I report distinctive external anatomical changes and the presence of a denser tissue medial to the tooth germs in specimens from the final portion of gestation, which can be interpreted as the first signs of baleen formation (baleen rudiments). Tooth germs are only completely resorbed just before the eruption of the baleen from the gums, and they are still present for a brief period with baleen rudiments. Skull shape development is characterized by progressive elongation of the rostrum relative to the braincase and by the relative anterior movement of the supraoccipital shield, contributing to a defining feature of cetaceans, telescoping. These data aid the interpretation of fossil morphologies, especially of those extinct taxa where there is no direct evidence of presence of baleen, even if caution is needed when comparing prenatal extant specimens with adult fossils. The ontogeny of other mysticete species needs to be analyzed before drawing definitive conclusions about the influence of development on the evolution of this group. Nonetheless, this work is the first step towards a deeper understanding of the most distinctive patterns in prenatal skull development of baleen whales, and of the anatomical changes that accompany the transition from tooth germs to baleen. It also presents comprehensive hypotheses to explain the influence of developmental processes on the evolution of skull morphology and feeding adaptations of mysticetes.

Predicting large-scale habitat suitability for cetaceans off Namibia using MinxEnt

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 619:149-167 (2019) - DOI: https://doi.org/10.3354/meps12934 Predicting large-scale habitat suitability for cetaceans off Namibia using MinxEnt P. De Rock1, S. H. Elwen1,2, J. P. Roux3,4, R. H. Leeney5, B. S. James1, V. Visser6,7, M. J. Martin2, T. Gridley1,6,* 1Sea Search Research and Conservation NPC, 4 Bath Rd, Muizenberg, Cape Town 7945, South Africa 2Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, South Africa 3Lüderitz Marine Research, Ministry of Fisheries and Marine Resources, Lüderitz, Namibia 4SEACODE, Box 583, Lüderitz, Namibia 5Natural History Museum, Cromwell Road, Kensington, London SW7 5BD, UK 6Statistics in Ecology, Environment and Conservation, Department of Statistical Sciences, University of Cape Town, Rondebosch, Cape Town 7701, South Africa 7African Climate and Development Initiative, University of Cape Town, Rondebosch 7701, South Africa *Corresponding author: tessgridley@yahoo.co.uk ABSTRACT: Knowledge of the occurrence and distribution of cetaceans is particularly important for conservation and management, but is still limited within Namibian waters. We collated 3211 cetacean records from the Namibian Exclusive Economic Zone (EEZ) for the period 2008 to 2016 and applied the principle of minimum cross entropy (MinxEnt) to predict habitat suitability. MinxEnt is a generalised form of maximum entropy modelling that allows incorporation of additional information such as sampling bias. The habitat suitability of 9 cetacean species or species groups (5 odontocete species, 2 mysticete species and 2 taxonomic groups: pilot whales Globicephalus spp. and balaenopterids Balaenopteridae spp.) were predicted per season, in relation to environmental variables likely to drive cetacean presence: sea surface temperature, chlorophyll a concentration, water depth or distance to shore, seabed slope and habitat complexity. The environmental variable which most frequently influenced habitat suitability was depth, which was the main environmental driver for bottlenose dolphin Tursiops truncatus, humpback Megaptera novaeangliae and southern right whales Eubalaena australis. Further, Heaviside’s dolphin Cephalorhynchus heavisidii habitat was best predicted by distance to shore in all seasons, while common dolphin Delphinus delphis and the balaenopterid group habitats were best predicted by habitat complexity, and sperm whale Physeter macrocephalus habitats by chlorophyll a concentration. We identify distinct spatial patterns in habitat suitability for different species and provide baseline maps which can be used by managers of wildlife resources. KEY WORDS: Cetacean · Dolphin · Habitat modelling · Habitat suitability · Marine protected area · Marine spatial planning · MaxEnt · Whale Full text in pdf format Supplementary material PreviousNextCite this article as: De Rock P, Elwen SH, Roux JP, Leeney RH and others (2019) Predicting large-scale habitat suitability for cetaceans off Namibia using MinxEnt. Mar Ecol Prog Ser 619:149-167. https://doi.org/10.3354/meps12934 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 619. Online publication date: June 04, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.